Process for production of hydroxygbenzoic acids

ABSTRACT

The present invention provides a method for producing a hydroxybenzoic acid compound comprising, dehydrating a phenol compound and an alkaline metal compound to form the alkaline metal salt of the phenol compound and reacting the alkaline metal salt and carbon dioxide, wherein the dehydrating step is conducted by reacting the alkaline metal compound with an excess amount of the phenol compound at a temperature of 160° C. or above. According to the method of the present invention, the hydroxybenzoic acid compound can be obtained by simple steps with low cost without using an expensive aprotic polar organic solvent. The provided method can produce highly pure hydroxybenzoic acid compound comprising little by-products in high yield.

FIELD OF THE INVENTION

The present invention relates to a method for preparing a hydroxybenzoicacid compound.

BACKGROUND OF THE INVENTION

As a method for preparing a hydroxybenzoic acid compound, a solid-gasphase reaction to react phenol potassium with carbon dioxide, which isknown as Kolbe-Schmitt reaction, has conventionally been used. TheKolbe-Schmitt reaction, however, has some problems such as the longreaction time which is required due to the solid-gas phase reaction, thegreat loss of the reaction material because of side reaction due to thethermal non-uniformity of the reaction and the fluctuate of the yieldbecause of the difficulty in controlling the reaction. In recent years,in order to overcome those problems of the solid-gas phase Kolbe-Schmittreaction, liquid-phase methods wherein the reaction is conducted in asolvent or as slurry are proposed from the industrial viewpoints.

For example, Japanese Patent Application Laid Open No. 3-90047 disclosesa method for preparing 3,5-dialkyl salicylic acid comprising heating2,4-dialkylphenol and alkaline metal hydroxide in a mixed solvent ofhydrocarbon and 1,3-dimethyl-2-imidazolidinone to give anhydrous2,4-dialkylphenol alkaline metal salt through azeotropic dehydration andreacting said metal salt with carbon dioxide in said mixed solvent togive 3,5-dialkyl salicylic acid.

Though the use of an aprotic polar organic solvent such as1,3-dimethyl-2-imidazolidinone in the reaction makes it possible toattain a high reaction yield, said method has some problems incollecting the product from the reaction mixture and recovering thesolvent. That is, despite of the high reaction yield, 3,5-dialkylsalicylic acid alkaline metal salt can not be sufficiently collected bymeans of crystallization because of the high solubility of the alkalinemetal salt to the aprotic polar organic solvent. In addition, though theaqueous solution of 3,5-dialkyl salicylic acid alkaline metal saltobtained by the reaction contains a large amount of aprotic polarorganic solvent, the expensive aprotic polar organic solvent isdifficult to collect because it transfers into the filtrate after theacid precipitation method.

In order to solve the above problems, Japanese Patent Application LaidOpen No. 10-231271 proposes a method for preparing a hydroxybenzoic acidcompound wherein an aprotic polar organic solvent is used as reactionsolvent for the reaction between a phenol compound and an alkaline metalcompound, characterized in that the molar ratio of the phenol compoundto the total amount of the alkaline metal compound and the aprotic polarorganic solvent is larger than 1.

However, the yield of hydroxybenzoic acid obtained by said method, whichuses an excess amount of the phenol compound over the total amount ofthe alkaline metal compound and the aprotic polar solvent, is notsufficient. There is also a problem of side product such as a dimer ofthe phenol compound produced during the Kolbe-Schmitt reaction in thepresence of an aprotic polar organic solvent and therefore, it isdifficult to obtain high-purity hydroxybenzoic acids.

Furthermore, use of expensive aprotic polar organic solvent results inhigh cost.

SUMMARY OF THE INVENTION

An object of the present invention is providing a method for preparing ahydroxybenzoic acid compound with high yield without using an expensiveaprotic polar organic solvent.

The present invention provides a method for producing a hydroxybenzoicacid compound comprising, dehydrating a phenol compound and an alkalinemetal compound to form an alkaline metal salt of phenol and reacting thealkaline metal salt and carbon dioxide, wherein the dehydrating step isconducted by reacting said alkaline metal compound with an excess amountof the phenol compound, which is in excess of the alkaline metalcompound, at a temperature of 160° C. or above.

According to the method of the present invention, by using an excessamount of the phenol compound over the alkaline metal compound, thedehydration between the phenol compound and the alkaline metal compoundis promoted and consequently, the alkaline metal salt of the phenolcompound can be obtained with high yield and the remaining phenol can beused again as a solvent.

In the present specification and claims, “excess” amount of the phenolcompound means that the amount of the phenol compound is two or moremolar parts per 1 molar part of the alkaline metal compound. In thepresent invention, the amount of the phenol compound is preferably 2-30molar parts, more preferably 3-15 molar parts and even more preferably4-10 molar parts per 1 molar part of the alkaline metal compound. Incase where the amount of the phenol compound is less than 2 molar parts,the alkaline metal salt of the phenol compound will precipitate andinterfere with homogeneous stirring. Using more than 30 molar parts ofphenol is permissible, but it will not bring about better result thanusing less amount of phenol and therefore, it is not economical.

In the method of the present invention, dehydrating of the alkalinemetal compound and the phenol compound is conducted at a temperature of160° C. or above and preferably at 180-300° C. If the temperature duringdehydration is lower than 160° C., the alkaline metal salt hardly beformed and water produced by the dehydration of the phenol and thealkaline metal compound can not be sufficiently removed. On thecontrary, if the temperature during the dehydration step is higher than300° C. which is above the boiling point of the phenol, the phenol mightbe distilled out of the reaction system and the alkaline metal salt ofphenol might be thermally decomposed due to such a high temperature.

In the present invention, the phenol compound preferably used as astarting material is represented by formula (I):

wherein, R is selected from the group consisting of hydrogen atom,linear or branched chain C1-20 alkyl, C1-20 alkenyl and C1-20 alkoxygroups; n is an integer from 1 to 4.

Among the above, alkyl substituted phenols (R=alkyl group), preferablydialkyl substituted phenols are suitably used for the method of thepresent invention because of their high reaction selectivity and highreaction yield. Examples of alkyl groups suitable for the substituentsare methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl,n-octyl and tert-octyl.

Examples of alkyl substituted phenols preferably used in the presentinvention are o-cresol, p-cresol, m-cresol, 2,6-dimethylphenol,3,5-dimethylphenol, 2,5-dimethylphenol, o-isopropylphenol,2,6-di-tert-butylphenol, 2,4-di-tert-butylphenol,2,5-di-tert-butylphenol, 4-n-octylphenol and 4-tert-octylphenol.

In case there are two or more substituents on the phenol, thesubstituents may be the same or different.

A preferable alkaline metal compound used in the present invention issodium hydroxide or potassium hydroxide. In particular, sodium hydroxideis preferable because it allows rapid dehydration and is inexpensive.

In the method of the present invention, water produced during thedehydrating step is preferably removed from the reaction system.

In order to promote the dehydrating step, an azeotropic dehydrationagent may be added to the reaction mixture. In general, one or more ofhydrocarbon type solvents which are selected from the group consistingof aliphatic hydrocarbons such as octane, nonane, decane, undecane,dodecane, ligroin and kerosene; aromatic hydrocarbons such as benzene,toluene, xylene, mesitylene, ethylbenzene, cumene, diphenylether andnaphthalene; and halogenated hydrocarbons such as chlorobenzene,o-dichlorobenzene, and p-dichlorobenzene are used as an azeotropicdehydration agent. The amount of the azeotropic dehydration agent usedin the reaction may vary depending on the amount of water contained inthe reaction system, and in general, the amount of the azeotropicdehydration agent used may be 2-10 parts by weight per 1 part by weightof water contained in the system.

In the method of the present invention, the liquid state substitutedphenol acts as solvent and therefore, it is not necessary to add anyother solvent in the step to obtain an alkaline metal salt of the phenolcompound. However, the case where an additional solvent other than thesubstituted phenol is used is also included in the scope of the presentinvention. Solvents other than the phenol compound used in thedehydrating step may be any of those other than aprotic polar organicsolvents. Examples of such solvents are light oil, kerosene, petrol,lubrication oil, white oil, alkylbenzene, alkylnaphthalene, diphenyl,diphenylalkane, alkyldiphenyl, triphenyl, hydrogenated triphenyl,diphenylether, alkylphenylether, alkyldiphenylether, high boiling pointhigher alcohols such as iso-octyl alcohol and a mixture thereof.

In the method of the present invention, dehydrating step is carried outunder inert gases atmosphere such as nitrogen, helium and argon gas.

In the method of the present invention, the alkaline metal salt of thephenol compound obtained by the dehydrating step is subjected to thenext step, i.e. reacting the same with carbon dioxide.

The reaction of the alkaline metal salt of the phenol compound andcarbon dioxide is curried out in an autoclave under the carbon dioxidepressure of preferably 2.0-10 kgf/cm² (G), more preferably 4.0-8.0kgf/cm² (G) at a reaction temperature preferably of 160-300° C., andmore preferably of 170-290° C. The reaction time may vary depending onthe carbon dioxide pressure and the reaction temperature, and ingeneral, it may be 1-6 hrs, and preferably 1-4 hrs.

Into thus obtained reaction mixture comprising the alkaline metal saltof the hydroxybenzoic acid compound, water is added and then the mixtureis separated into the solvent and water phases. Next, the water phase,i.e. an aqueous solution containing the alkaline metal salt of thehydroxybenzoic acid compound is added with an acid to precipitate thehydroxybenzoic acid compound. The precipitates may be collected byfiltration and centrifugation to give crystalline hydroxybenzoic acidcompound.

The solvent phase separated from the reaction mixture in this example ismainly consisting of the starting phenol compound and therefore, thesolvent phase may be used again as starting phenol compound directly or,if necessary, after purified by, such as, filtration, distillation orcarbon treatment.

Non limiting examples of the hydroxybenzoic acid compounds produced bythe method of the present invention are3,5-di-tert-butyl-4-hydroxybenzoic acid,3,5-di-tert-butyl-2-hydroxybenzoic acid, 3-methyl-4-hydroxybenzoic acid,2,6-dimethyl-4-hydroxybenzoic acid, 2-ethyl-4-hydroxybenzoic acid and3,5-diethyl-4-hydroxybenzoic acid. Among the above,3,5-di-tert-butyl-4-hydroxybenzoic acid produced from2,6-di-tert-butylphenol and 3,5-di-tert-butyl-2-hydroxybenzoic acid2,4-di-tert-butylphenol are preferable because they are obtained withhigh yields.

According to the method of the present invention, highly purehydroxybenzoic acid compound can be obtained with low amount ofside-products and with high yields. Moreover, the method of the presentinvention makes it possible to produce the hydroxybenzoic acid compoundat low cost with simple steps without using an expensive aprotic polarsolvent. Furthermore, the solvent phase separated from the reactionmixture in the method contains little amount of by-products andtherefore, it can be used again as the starting phenol compound.

The hydroxybenzoic acid compound produced by the method of the presentinvention can be used as a raw material for producing ultravioletabsorber, antioxidant and the like which are contained in plastics suchas polypropylene.

The present invention is further described in reference to the followingexamples. The examples are intended to illustrate the invention and arenot to be construed to limit the scope of the invention.

EXAMPLE 1

432.6 g (2.1 moles) of 2,6-di-tert-butylphenol and 25 g (0.3 mole) of48% aqueous sodium hydroxide were fed in an autoclave having 1 Lstainless-steel vessel equipped with a magnetic stirrer, a thermometer,pressure gauge and water-separator. The reaction mixture was heated to210° C. under nitrogen gas flow and at this temperature, dehydration wasconducted for 4 hrs. Next, nitrogen gas in the vessel was replaced withcarbon dioxide gas and carboxylation was carried out at 210° C. underthe pressure of 6 kgf/cm² (G) with stirring for 2 hrs. After thereaction was completed, the reaction mixture was cooled to 60° C. and800 g of water was added thereto. The obtained mixture was heated to 65°C. and the mixture was separated into the water and solvent phases.

To thus obtained water phase, 73% aqueous sulfuric acid was added toprecipitate crystal and the crystal was filtrated, washed with water anddried. As a result, 60 g of powdery 3,5-di-tert-butyl-4-hydroxybenzoicacid was obtained. The yield to the fed amount of sodium hydroxide was80%.

EXAMPLE 2

To the solvent phase removed from the water phase in example 1, 51.5 g(0.25 mole) of 2,6-di-tert-butylphenol and 25 g (0.3 mole) of 48%aqueous sodium hydroxide were added. According to the similar methodwith example 1, 59.3 g powdery 3,5-di-tert-butyl-4-hydroxybenzoic acidwas obtained. The yield to the fed amount of sodium hydroxide was 79%.

It was confirmed that the solvent phase separated from the reactionmixture in example 1 did contain little amount of side-products andcould be used again as starting material of the method of the presentinvention.

EXAMPLE 3

By the same method as Example 1 except that dehydrating step wasconducted at 180° C., 37.5 g of powder of3,5-di-tert-butyl-4-hydroxybenzoic acid was obtained. The yield to thefed amount of sodium hydroxide was 50%.

COMPARATIVE EXAMPLE 1

The same method as Example 1 was carried out except that dehydratingstep was conducted at 150° C. In the comparative example 1, noprecipitation was generated by adding 73% aqueous sulfuric acid and3,5-di-tert-butyl-4-hydroxybenzoic acid could not be obtained.

EXAMPLE 4

The same method as Example 1 was carried out except that2,4-di-tert-butylphenol was used instead of 2,6-di-tert-butylphenol, 60g of powdery 3,5-di-tert-butyl-2-hydroxybenzoic acid was obtained. Theyield to the fed amount of sodium hydroxide was 80%.

INDUSTRIAL APPLICABILITY

The present invention provides a method for producing highly purehydroxybenzoic acid compound with high yield and little side-products.The present invention makes it possible to produce hydroxybenzoic acidcompound by simple steps at low cost without using expensive aproticpolar organic solvent.

1. A method for producing a hydroxybenzoic acid compound comprising,dehydrating a phenol compound and an alkaline metal compound to form thealkaline metal salt of the phenol compound and reacting the alkalinemetal salt and carbon dioxide, wherein the dehydrating step is conductedby reacting the alkaline metal compound with an excess amount of thephenol compound, which is in excess of the alkaline metal compound, at atemperature of 160° C. or above.
 2. The method of claim 1, wherein saiddehydrating step is conducted at a temperature of 180-300° C.
 3. Themethod of claim 1, wherein 2-30 parts by mole of the phenol compound isreacted per 1 part by mole of the alkaline metal compound.
 4. The methodof claim 1, wherein the phenol compound is a compound represented byformula (I):

wherein, R is selected from the group consisting of hydrogen atom,linear or branched chain C1-20 alkyl, C1-20 alkenyl and C1-20 alkoxygroups; n is an integer from 1 to
 4. 5. The method of claim 1, whereinthe phenol compound is an alkyl substituted phenol.
 6. The method ofclaim 1, wherein the phenol compound is a di-alkyl substituted phenol.7. The method of claim 5, wherein, the alkyl group of the alkylsubstituted phenol is selected from the group consisting of methyl,ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl and octyl.8. The method of claim 1, wherein the phenol compound is selected fromthe group consisting of o-cresol, p-cresol, m-cresol,2,6-dimethylphenol, 3,5-dimethylphenol, 2,5-dimethylphenol,o-isopropylphenol, 2,6-di-tert-butylphenol, 2,4-di-tert-butylphenol,2,5-di-tert-butylphenol, 4-n-octylphenol and 4-tert-octylphenol.
 9. Themethod of claim 1, wherein the phenol compound is2,6-di-tert-butylphenol or 2,4-di-tert-butylphenol and saidhydroxybenzoic acid is 3,5-di-tert-butyl-4-hydroxybenzoic acid or3,5-di-tert-butyl-2-hydroxybenzoic acid.
 10. The method of claim 1,wherein the alkaline metal compound is sodium hydroxide or potassiumhydroxide.
 11. The method of claim 6, wherein, the alkyl group of thealkyl substituted phenol is selected from the group consisting ofmethyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl andoctyl.